(1) Field of the Invention
The invention relates to an arrangement for the potential-free measurement of currents according to the preamble of claim 1.
(2) Description of Related Art
Prior art arrangements of this type measure currents by detecting a magnetic differential field, or a magnetic field gradient, respectively, generated by a current in a substantially U-shaped conductor unit the limbs of which may be referred to as primary conductors (WO 00/11482, DE 4300605 C2, U.S. Pat. No. 5,548,208).
The magnetic differential field, or the magnetic field gradient, respectively, penetrates a differential field sensor, or a gradiometer, respectively, which generates a signal voltage corresponding to the magnetic differential field, or the magnetic field gradient, respectively, without being galvanically connected with the primary circuit. Thereby, a measuring system is desired without any elaborate magnetic flow conduction while the influence of magnetic interference fields is nonetheless minimized.
Sensors based on magneto resistive effects such as the anisotropic magneto resistive effect (AMR) or the gigantic magneto resistive effect (GMR) may be used in particular as suitable differential field sensors. Such sensor systems on the basis of the colossal magneto resistive effect (CMR) or of the tunnel magneto resistive effect (TMR) are conceivable as well.
In the case of arrangements for the potential-free measurements of currents of the kind referred to in the beginning, it is the task as mentioned before to reduce a sensibility vis-à-vis external magnetic interference fields which may disturb the detection of the magnetic differential field, or the field gradient, respectively, relevant for the measurement. The external magnetic fields may, inter alia, be caused by eddy currents which, on their part, are induced in adjoining metal parts by the magnetic field of the current to be measured, referred to as primary current. In order to reduce the frequency-depending measuring errors caused thereby, it has already been known in an arrangement of the kind referred to in the beginning to adjust the cross-sectional area and the form as well as the material selection of the primary conductors and their distance from particularly shaped neighboring metal parts, if any, and the magnetic field sensitive measuring devices, particularly sensors, so that the influences of different electro-dynamic effects, particularly of the induction of eddy currents in the neighboring metal parts, largely compensate each other (DE 19819470 A1, particularly FIG. 4). In detail, an arrangement of this kind is realized by a conductor unit made in U-shape on which a dielectric plate is fastened which carries a magnetic field measuring device and causes a galvanic separation. Above and below this arrangement, the above-referenced neighboring metal parts, particularly plates, are disposed, spaced in predetermined order.